Bituminous tar sands are siliceous materials which are impregnated with a highly viscous crude hydrocarbon material. The largest and most important deposits of these sands are the Athabasca tar sands found in northern Alberta, Canada. These sands underlay more than 13,000 square miles at depths of 0 to 2000 feet. Total recoverable reserves after extraction and processing are estimated at more than 300 billion barrels of oil. The tar sands are mixtures of sand, water, and bitumen. The sand component is predominately quartz, particles of which are water-wet. A film of bitumen is closely associated with the particles, surrounding the sand grains and somewhat filling the void volume among them. This bitumen makes up from about 5 to 21 percent by weight of the total weight of tar sands with a typical content of 13 weight percent. The tar sands also contain clay and silt. Elemental analyses of the tar sands solids have also indicated the presence of zirconium and titanium.
To date, emphasis on development of bituminous tar sands has been placed in the area of the production of a synthetic crude oil. Thus, for example, the cold water process and the hot water process are well-known methods for the separation and recovery of bitumen from tar sands. In the cold-water method, separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water wth a surface agent added, or a solution of neutral salt in water. The combined mass is then subjected to a pressure or gravity separation.
In the hot water method, the bituminous tar sands are jetted with steam and mulled with a minor amount of hot water at temperatures in the range of about 150.degree. to 200.degree. F. In the separation cell, sand settles to the bottom as tailings and bitumen rises to the top in the form of an oil froth. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenger step may be conducted on the middlings layer from the primary separation step to recover additional amounts of bitumen therefrom. This step usually comprises aerating the middlings as taught by K. A. Clark, "The Hot Water Washing Method", Canadian Oil and Gas Industries 3,46 (1950). The froth from the primary separation and the froth from the scavenger step can be combined, diluted with naphtha, and centrifuged to remove more water and residual mineral. The naphtha is then distilled off and the bitumen is coked to a high quality crude suitable for further processing. The hot water process is described in detail in Floyd et al., Canadian Pat. No. 841,581 issued May 12, 1970.
It has been discovered that the heavy metals, such as zirconium and titanium ores, are selectively separated from less dense metals by the above hot water process. In particular, zirconium and titanium are recovered as waste products from high speed centrifugation of bitumen froth extracted by hot water from tar sands.
Because titanium and zirconium are present in tar sands as salts or oxides in such small quantities, little effort thus far has been directed toward the recovery of these valuable minerals or their ores from the sands. It has been reported that tar sands solids contain about 0.05 weight percent elemental zirconium and 0.21 weight percent elemental titanium. (See Bowman, "Molecular and Interfacial Properties of Athabasca Tar Sands", 7th World Petroleum Conference, at page 590) Now, however, it has been found that zirconium as zircon and titanium as rutile are surprisingly highly concentrated in the sand separated from diluted bitumen in the centrifuging step of the hot water process.
The zirconium and titanium, which are the valuable metals in the tar sand minerals, are normally found in the form of zircon, ilmenite, anatase, and rutile. Zircon and rutile are the most valuable forms of the minerals in the mixture. When the mixture of heavy minerals is recovered from the waste stream of the hot water extraction process, the minerals are selectively wetted and in fact in many instances completely coated with bitumen. In order to separate the valuable minerals such as rutile and zircon from the less valuable minerals such as anatase and ilmenite, the minerals should be clean and dry since electrodynamic processing is employed. Procedures which at first glance would appear to be effective are calcining and/or roasting the bitumen-coated minerals to remove the hydrocarbons therefrom. However, these procedures have been found ineffective in that the roasting process, because of the high temperatures generated in burning off the hydrocarbon materials, alters the minerals in a manner that the electrodynamic processes no longer serve to provide an efficient means of separating the minerals selectively.
One process proposed in the prior art for recovering heavy metals from bituminous tar sands is proposed in U.S. Pat. No. 3,656,938 issued Apr. 18, 1972 to Penzes. The process provided in this patent includes air flotation of the minerals in a caustic solution. It is pointed out that large volumes of caustic are necessary in order to strip the bitumen from the minerals and subsequently the minerals must be washed to remove the caustic, all of which is both expensive and time-consuming. Thus, the prior art provides no distinctly attractive process for removing bitumen from the heavy minerals found in tar sands in a way which will provide for subsequent separation of those minerals into valuable products in an economic manner. A means to effectively cleanse heavy minerals from hydrocarbon materials found thereon to provide a mineral product suitable for separation by standard known methods has now been discovered.